Μετά την πρώτη απογοήτευση ήρθε μεγάλη ανακούφιση, γιατί το πρόβλημα δεν ήταν σοβαρό.

Because μετά meaning after is followed by the accusative in Modern Greek.

So:

• μετά = after
• την πρώτη απογοήτευση = the first disappointment

All three words are in the accusative feminine singular:

• την = the
• πρώτη = first
• απογοήτευση = disappointment

So μετά την πρώτη απογοήτευση literally means after the first disappointment.

It can be understood as either first or initial, depending on context.

In this sentence, την πρώτη απογοήτευση most naturally means:

• the first disappointment
• or more idiomatically in English, the initial disappointment

Greek often uses πρώτος / πρώτη / πρώτο in places where English might prefer initial.

Because απογοήτευση is a feminine noun in Greek. Nouns in Greek have grammatical gender, and adjectives/articles must agree with them.

So:

• η απογοήτευση = disappointment
• την απογοήτευση = disappointment (accusative)

That is why the article and adjective are also feminine:

• την πρώτη απογοήτευση

Ήρθε is the aorist form of έρχομαι (to come).

Here it means:

• came
• or more naturally in English in this sentence, was followed by / there came

So:

• ήρθε μεγάλη ανακούφιση = great relief came / there was great relief

The aorist is commonly used for a single completed event in the past.

It is a very natural Greek way to express that a feeling or state appeared afterward.

So ήρθε μεγάλη ανακούφιση literally means:

• great relief came

But in more natural English, you might translate it as:

• there was great relief
• great relief followed
• then came great relief

Greek often uses motion verbs like έρχομαι with abstract nouns in a way that sounds more literary or expressive in English.

Because Greek does not always need an article where English might use one.

μεγάλη ανακούφιση means:

• great relief

It is indefinite here, not the great relief.

Compare:

• ήρθε μεγάλη ανακούφιση = great relief came
• ήρθε μια μεγάλη ανακούφιση = a great relief came / there came a great relief

Leaving out the article can sound very natural with abstract nouns like ανακούφιση.

Both are possible, because Greek word order is flexible.

The sentence has:

• ήρθε μεγάλη ανακούφιση

This is a natural way to present what happened next: relief came.

If you said:

• μεγάλη ανακούφιση ήρθε

that would put more emphasis on great relief itself.

So the chosen order is mainly about flow and emphasis, not a change in basic meaning.

It is in the nominative, because it is the subject of ήρθε.

Forms:

• η μεγάλη ανακούφιση = nominative
• τη μεγάλη ανακούφιση = accusative

In the sentence, the article is omitted, but the noun phrase is still nominative:

• ήρθε μεγάλη ανακούφιση

Yes, γιατί and επειδή can both mean because.

In this sentence:

• γιατί το πρόβλημα δεν ήταν σοβαρό = because the problem was not serious

Γιατί is extremely common in everyday Greek and sounds very natural here.

Very roughly:

• γιατί = common, versatile, everyday
• επειδή = also common, sometimes a bit more explicitly causal or slightly more formal

In this sentence, either would work.

Ήταν is the standard past form of είμαι (to be) used here.

• δεν ήταν σοβαρό = it was not serious

You may also hear ήτανε in speech, but ήταν is the normal standard written form.

This is the imperfect, which is used for states, descriptions, or ongoing background in the past. Since the sentence describes the condition of the problem, ήταν is the natural choice.

Because the sentence combines:

1. a completed event
2. a background state

So:

• ήρθε μεγάλη ανακούφιση = a completed event: great relief came
• το πρόβλημα δεν ήταν σοβαρό = a state in the past: the problem was not serious

This is a very common Greek pattern:

• aorist for the event
• imperfect for the situation or description behind it

Το πρόβλημα is neuter singular nominative, because it is the subject of ήταν.

• το πρόβλημα = the problem

σοβαρό is also neuter singular nominative, because it agrees with πρόβλημα and functions as a predicate adjective:

• σοβαρό = serious

So:

• το πρόβλημα δεν ήταν σοβαρό = the problem was not serious

Because πρόβλημα is a neuter noun in Greek.

Its article shows that:

• το πρόβλημα = the problem

That is why the adjective is also neuter:

• σοβαρό

Greek agreement is very important, so the gender/number/case of the noun affects the form of the adjective.

Yes. Σοβαρός / σοβαρή / σοβαρό usually means:

• serious
• sometimes grave, depending on context

Here the most natural translation is:

• the problem was not serious

In standard Greek punctuation, yes, it is normal to place a comma before a subordinate clause introduced by γιατί when it means because.

So this is standard and natural:

• ..., γιατί το πρόβλημα δεν ήταν σοβαρό.

It helps separate the main statement from the explanation.

Yes. A very close translation is:

• After the initial disappointment, great relief came, because the problem was not serious.

But more natural English might be:

• After the initial disappointment, there was great relief because the problem was not serious.
• After the first disappointment came great relief, because the problem was not serious.

The Greek wording is slightly more expressive than plain English, especially with ήρθε μεγάλη ανακούφιση.

It is mostly neutral standard Greek, but ήρθε μεγάλη ανακούφιση gives it a slightly more polished or narrative feel than a very plain everyday version.

A more everyday phrasing could be something like:

• Μετά την πρώτη απογοήτευση, νιώσαμε μεγάλη ανακούφιση...
• Μετά την πρώτη απογοήτευση, υπήρξε μεγάλη ανακούφιση...

But the original sentence is completely natural and standard.